Conventionally, when sensitive bodies are to be exposed over a wide range by means of an optical scanner, it has been required that the polygon mirror, scanner lens and/or other optical parts used be suitably upsized, or that to keep high image quality the parts precision and accuracy be maintained. Accordingly, as is disclosed in Japanese Patent Application Laid-Open No. 161778-1991 (hereunder called conventional example 1), there is provided a system whereby the range of exposure of sensitive bodies is divided, each division being fitted with a downsized optical scanner to carry out scanning and exposure. Under this system of conventional example 1, however, environmental changes and otherwise consequential deviations in parts precision or in optical magnification induce optical scanners to unfavorably overlap in the range of exposure, a defect which in the images produced is marked by the prominence of the boundaries of division.
Thereupon, in the Patent Specification No. 2,636,984 (hereunder called conventional example 2) is given a proposition that every scanning region be provided with overlapped areas in which their different pixels are intermixed to render the divided boundaries inconspicuous.
Further, in Japanese Patent Application Laid-Open No. 239613-1998 (hereinafter referred to as conventional example 3), where a system is introduced under which divided regions are sequentially recorded by using an optical scanner, it is proposed that in the connected (boundary) regions the fast scanning lines in partly drawn patterns on both sides of connection be linked up and synthesized at random points so as to randomly disperse the joints (seams) in the scanning regions to thereby make the joints inconspicuous.
Furthermore, Japanese Patent Application Laid-Open No. 161778-1991 and Japanese Patent Application Laid-Open No. 19438-2000 disclose a system in which the range of exposure of sensitive bodies is divided, with each division installed with a downsized optical scanner to conduct scanning and disclosure. Under this system, toners and dust particulates tend with age to get wind-borne and scatter to spoil the optical scanning system, resulting in variations with separate optical scanners in the intensity of irradiation that reaches the sensitive body. This has the defect of causing the photographic density to differ at the boundaries and the quality of image to downgrade. To counter this, dust-preventive panes are provided, and as soon as spoiled, they are replaced or cleaned in seeking to recover the irradiation intensity.
In the conventional examples 2 and 3 mentioned above, however, before reprinting is made, an allocation is carried out with regard to whether or not pixels are to be recorded selectively, in pixel units, from among all image data involving a single, entire scanning. Because of this, when a plurality of unit modules are optically scanned in parallel, respective unit modules are recorded in synchronism, whilst the timing of a start made on the recording is asynchronous, a situation that necessitates a separate provision of the means to the selection of the pixels recorded above. This poses a problem of the control system becoming complicated.